3)3x +5 2x + 7. x²-4 x²-4'

3) $$\frac{3x + 5}{x^2 - 4} - \frac{2x + 7}{x^2 - 4} = \frac{3x + 5 - (2x + 7)}{x^2 - 4} = \frac{3x + 5 - 2x - 7}{x^2 - 4} = \frac{x - 2}{x^2 - 4} = \frac{x - 2}{(x - 2)(x + 2)} = \frac{1}{x + 2}.$$

Ответ: $$\frac{1}{x+2}$$